Process of making cyanoalkylsilanes



w s atent Qfilice 3,045,292 Patented July 24, 1962 3,tl46,292 PROCES F MAKlNG CYANGALKYLSILANES Roscoe A. Pike, Holden, Mass, assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed Dec. 30, 1959, Ser. No. 862,748 7 Claims. (Cl. 260-4482) This invention is directed to a process for making cyanoalkylsilanes containing three hydrolyzable groups attached to silicon and a cyano group interconnected to silicon through at least two carbon atoms of an alkyl group of two or more carbon atoms. More particularly, this invention relates to a process involving the reaction of alkene nitriles with silanes having hydrogen and three hydrolyzable groups attached to silicon in the presence of a tertiary disilyl amine catalyst.

It has heretofore been shown that when acrylonitrile is reacted with a silane having a .silanic hydrogen the silyl group of the silane bonds to that carbon atoms of the two olefinic carbon atoms which is interconnected to the cyano group through the lesser number of carbon atoms and the silanic hydrogen bonds to that carbon atom of the two olefinic carbon atoms which is interconnected to cyano group through the greater number of carbon atoms. The reaction taking place, for example, between acrylonitrile and trichlorosilane, is represented by the equation:

The process of this invention comprises reacting an alkene nitrile with a silane having one hydrogen and three hydrolyzable groups bonded to silicon in the presence of a tertiary disilyl amine of the formula:

wherein A is a monovalent hydrocarbon group or a hydrolyzable group and need not be the same throughout the same molecule, and R is a monovalent hydrocarbon group. Thus included are the N,N-bis(trialkylsilyl) -N-hydrocarbylamines, the N,N bis (trialkoxysilyl)-N-hydrocarbylamines and the N,N-bis (trihalosilyl) -N-hydrocarbylamines as depicted by the above formula where R is a monovalent hydrocarbon group and A is, respectively, alkyl, alkoxy and halogen. As used herein, the term hydrocarbyl designates a monovalent hydrocarbon group. Examples of these tertiary disilyl amines are and the like. Methods for preparing these amines are known in the art. In general they are prepared by reacting a silane having one silicon-bonded halogen atom with preferably at least three moles of a primary aliphatic hydrocarbon amine for each mole of silane in a solvent such as petroleum ether or isopropyl ether, at atmospheric pres sure and room temperature. Cooling, as by an ice bath, is employed when the temperature of reaction increases much above room temperature. This reaction forms the tertiary disilyl amine and an amine hydrohalide. The tertiary disilyl amines are isolated by filtering out the amine hydrohalide and distillation of the resulting filtrate through a packed column.

In carrying out the process of this invention the s-ilyl group of the silane starting material bonds to that carbon atom of the two olefinic carbon atoms of the alkene nitrile starting material which is interconnected to the cyano group through the greater number of carbon atoms and the silanic hydrogen atoms of the silane starting material bonds to that carbon atom of the two olefinic carbon atoms of the nitrile starting material which is interconnected to the cyano group through the lesser number of carbon atoms. The reaction taking place is represented by the in following equation wherein acrylonitnile is employed as exemplifying the alkene nitrile starting material and HSiX (X being a hydrolyzable group) represents the silane starting material:

catalyst 1; H2O=GHON HSiX OH?- HON SiX3 The process is carried out by forming a mixture of the alkene nitrile, the silane, HSiX and the amine catalyst and heating the mixture to a temperature sufficiently elevated to bring about reaction of the nitrile and silane. When either one or both of the starting materials are gaseous at the reaction temperature a closed system, in accordance with techniques commonly employed in the art to maintain the concentrations of the starting materials at suflicient levels for providing the intimate reactive contact necessary for reaction, can be used. The process is advantageously carried out in pressure vessels or bombs in order to facilitate observation and favor closer control of reaction conditions, particularly when the one or both of the starting materials is gaseous at the reaction temperature. Continuous process systems can also be employed in carrying out the process.

Catalyst concentration is not narrowly critical and can be varied over a wide range. Thus, :as little as 0.5 weight percent and as much as 10 weight percent of catalyst based on the combined weights of the starting materials are advantageously employed. Catalyst concentrat-ions outside of this range are operable in the process but do not provide any additional advantage. A preferable catalyst concentration range has been found to be 1.6 to 2.5 weight percent based on the combined weights of the starting materials.

Equimolar or stoichiometric amounts of the starting materials have been found to be entirely suitable in the process. An excess of one or the other starting material over the stoichimetric amount can also be employed but no commensurate gain is obtained thereby. A useful range of amounts of starting materials is about one-half to two moles of the alkene nitrile per mole of the silane.

The temperatures employed in the process can be varied over a wide range from 50 C. to 250 C. Temperatures outside this range can be employed, if desired, but to no noticeable advantage. Within this temperature range reaction times vary from one-half to ten hours. Reaction times of one to about three hours are advantageously used when the process is conducted at temperatures in the range of C. to C.

The mixture resulting after completion of the reaction contains the cyanoalkylsilane product, some unreacted nitrile and silane starting materials and other materials mainly believed to be polymeric substances. The cyanoalkylsilane product is advantageously recovered from this mixture by fractional distillation, preferably under reduced pressure. Other means of recovery are within the skill of workers in the art and can be employed. When fractional distillation is employed for recovery, the cyanoalkylsilane product is obtained as a cut or series of cuts at its characteristic boiling point under the distillation pressure employed. Other high boiling materials such as unreacted starting materials are removed as a series of cuts and a residue or heavies remain in the still pot. These heavies are believed to be various polymerization materials of the alkene nitrile and the silane starting material and represent a loss of starting material.

nitriles. Higher yields thus can be obtained employing such difunctional silanes and longer reaction times or higher temperatures or, alternatively, the starting materials saved from polymerizing can be recovered and reused to provide a substantial economy. A polymerization inhibitor known in the art to inhibit the polymerization of the alkene nitrile also can be used and thus reduce the amount of heavies obtained. Such polymerization inhibitors are 2,6-di-t-butylparacresol, hydroquinone, tbutylcatechol, t-butyl-4-methylphenol and the like.

The alkene nitriles used as starting materials in the process are known in the art. The alkene nitriles are represented by the formula, alkenyl-CN, and include acrylonitrile, methacrylonitrile, crotononitrile, allyl cyanide, methylallyl cyanide, 1-cyano-4-pentene, l-cyano- 3-butene, l-cyano-l-hexene and the like.

The silane starting materials are also known and are represented by the formula:

HSiX

wherein X represents a hdrolyzable group including alkoxy, aryloxy, acetoxy, halogen and the like. Prefered silane starting materials are the halosilanes and alkoxysilanes as shown by the formula wherein X is halogen or alkoxy. Illustrative of these silanes are trichlorohydrogensilane, triethoxyhydrogensilane, triacetoxyhydrogensilane, triphenoxyhydrogensilane and the like.

The cyanoalkylsilane products made by the process are represented by the formula:

where X is as previously defined, C,,H is a divalent alkane group, a is an integer of at least 2 and NC-- is interconnected to silicon through at least two carbon atoms of the divalent alkane group, C H Such cyanoalkylsilanes are illustrated by beta-cyanoethyltrichlorosilane, beta cyanoethyltriethoxysilane, gamma cyanopropyltrichlorosilane, beta-cyanopropyltriethoxysilane and the like. These cyanoalkylsilane products are useful in a variety of applications. They can be hydrolyzed and condensed to provide quick-curing resins useful in the manufacture of molded articles, protective coatings and laminates. The cyanoalkylchlorosilane products can be esterified with alkanols to provide the corresponding cyanoalkylalkoxysilanes which can be hydrogenated to give the corresponding arninoalkylalkoxysilanes. The aminoalkylalkoxysilanes are particularly useful as protective coatings for metal articles when applied to and cured on the surface of such articles.

One particular advantage of the use of tertiary disilyl amine catalysts in accordance with this invention is the ease with which catalyst contamination of the product can be avoided. The disilyl amines employed as catalysts herein are easily removed by esterification with an alcohol or by hydrolysis to convert the disilyl amine into a low boiling silylalkoxide or silanol by cleavage of the SI.N bond and stripping the low boiling material from the product. In many applications the removal of the dislyl amine catalyst is accomplished during the use of the cyanoalkylsilanes and no additional steps need be taken for catalyst removal. For example, when esterifying cyanoalkylchlorosilanes to the corresponding cyanoalkylalkoxysilanes the disilyl amine catalyst is removed in the ordinary course of the esterification. In many other applications the presence of the disilyl amine catalyst in the cyanoalkylsilane products is not at all objectionable.

The following example is presented. In this example, 1 weight percent of Ionol (a hindered phenol designated as 2,6-di-tertiary-butyl-4-methyl phenol) based on the combined weight of acrylonitrile and trichlorosilane was added to the reaction mixture to inhibit the polymerization of acrylonitrile. Although hindered phenols have previously been shown to catalyze the reaction of acrylonitrile and trichlorosilane to form beta-cyanoethyltri- A rs!) 3 923,200

chlorosilane, the yields of beta-cyanoethyltrichlorosilane herein obtained are far superior to yields obtained by processes wherein hindered phenols are employed without any tertiary disilyl amine. The Ionol inhibitor is unessential for obtaining high yields of beta-cyanoethyltrichlorosilane, the tertiary disilyl amine being indispensable.

Example Into a 300 cubic centimeter stainless steel pressure vessel were charged acrylonitrile and trichlorosilane (HSiCl in a one to one molar ratio, 1 weight percent of Ionol and 2 weight percent of N,N-bis(triethoxysilyl)-N-phenylweight percent being based on combined weights of acrylonitrile and trichlorosilane. The vessel was sealed and heated in a rocking furnace at C. for one hour. The vessel was then cooled and discharged of its liquid contents. The liquid contents were distilled through a Vigreaux column to give 35.6 weight percent of betacyanoethyltrichlorosilane based on the combined weight of acrylonitrile and trichlorosilane originally charged, and 22.8 weight percent of heavies on the same weight basis. In a procedure similar to that described in the example the following disilyl amines can be employed as catalysts in reacting trichlorosilane with acrylonitrile to produce beta-cyanoethyltrichlorosilane in high yields:

N,N-bis (triethoxysilyl) -N-ethylamine, N,N-bis (trimethylsilyl -N-butylamine, N,N-bis (trichlorosilyl) -N-phenylarnine, N,N-bis (triphenylsilyl) -N-hexylamine, and N,N-bis (triprop oxysilyl -N-cyclohexylamine.

What is claimed is:

1. A process for preparing a cyanoalkylsilane wherein the cyano group is interconnected to silicon through at least two carbon atoms, which comprises reacting an alkene nitrile with a silane having one silicon-bonded hydrogen atom and three silicon-bonded hydrolyzable groups selected from the class consisting of halogen, acetoxy groups, alkoxy groups and aryloxy groups in the presence of a tertiary disilyl amine of the formula:

where A is selected from the class consisting of alkyl groups, phenyl groups, a halogen atom and an alkoxy group and R is a monovalent hydrocarbon group selected from the class consisting of alkyl groups, cyclohexyl groups and phenyl groups.

2. A process as claimed in claim 1 wherein the alkene nitrile is acrylonitrile and the silane is trichlorosilane.

References Cited in the file of this patent UNITED STATES PATENTS Cohen et al Aug. 30, 1955 MacKenzie et a1. Oct. 25, 1955 

1. A PROCESS FOR PREPARING A CYANOALKYLSILANE WHEREIN THE CYANO GROUP IS INTERCONNECTED TO SILICON THROUGH AT LEAST TWO CARBON ATOMS, WHICH COMPRISES REACTING AN ALKENE NITRILE WITH A SILANE HAVING ONE SILICON-BONDED HYDROGEN ATOM AND THREE SILICON-BONDED HYDROLYZABLE GROUPS SELECTED FROM THE CLASS CONSISTING OF HALOGEN, ACETOXY GROUPS, ALKOXY GROUPS AND ARYLOXY GROUPS IN THE PRESENCE OF A TERTIARY DISILYL AMINE OF THE FORMULA: 